Take butter, yogurt, egg yolk, vinegar, cheddar cheese and dill in a large mixing bowl and whisk it well. Add baking powder, salt. Add flour slowly (to make very soft dough ) and start to knead.
Stop adding flour when you reach soft consistency.Make the dough one big ball, cover with plastic wrap. Place it in the refrigerator and let it rest for two hours.
Take some all purpose flour in a bowl and dip the dough ball into the flour. Dust a large, flat surface with the flour (dusting will keep the dough from sticking). Place the dough onto flat surface and roll the dough until it reaches 1/5" thickness with a roller pin. Keep dusting the dough with flour while you are rolling.
Preheat the oven 350F. Place a parchment paper on a baking sheet. Cut off the dough with a round cookie cutter.
Take the egg yolk and nigella-sesame seeds in a separate bowls.
Brush them first with egg yolk and then sprinkle sesame and nigella seeds on top.
Place them on the baking sheet.
Bake them golden brown.